The present invention relates to a high-pressure discharge lamp lighting apparatus adapted to be used in common for several kinds of AC voltages such as 100 V and 200 V.
Generally, an electric appliance of a high power-factor is required so that the electric appliance does not exert any bad influence on equipments in the electric power system used.
In order to make the power factor of an electric appliance high, it is general to use a boosting circuit called "active filter" for boosting an input voltage to a value not smaller than the maximum value of a source AC voltage.
For example, in the case of an input of 200 V, its maximum value is 200.times.2.sup.1/2 =282 V. Accordingly, if the input voltage is boosted to about 350 V by using an active filter in this case, the power factor is made higher. In the case of an input of 100 V, the input voltage is 100.times.2.sup.1/2 =141 V. Accordingly, if the input voltage is boosted to about 180 V by using an active filter in this case, the power factor is made higher.
In the case of an appliance adapted to be used in common for 100 V/200 V, the input voltage is, however, boosted to about 350 V by an active filter even when the appliance is used with AC 100 V. Since the excessive boosting increases the loss in the active filter portion, the conversion efficiency in use with AC 100 V is worsened in comparison with the conversion efficiency in use with AC 200 V. The lighting apparatus becomes large-sized and expensive because it must be equipped with a radiation fin corresponding to the low conversion efficiency in use with 100 V.
As a conventional apparatus to solve this problem, a discharge lamp lighting apparatus is disclosed, for example, in JP-A-9-55296.
In the disclosed apparatus, the boosted voltage in loaded-state of the active filter in the case of an input of 100 V is reduced to a value lower than that in the case of an input of 200 V in order to obtain the same conversion efficiency even in use with 100 V as that in use with 200 V.
However, the apparatus according to JP-A-9-55296 has a problem that the starting property is lowered in use with 100 V.
The reason why the starting property is lowered will be described with reference to FIG. 6. FIG. 6 is a voltage-current characteristic graph of gas discharge appeared on p. 156 of "Lighting Handbook" (edited by the Illumination Engineering Institute of Japan, issued by OHM-sha Ltd., 1994/10/30) and shows a state of gas discharge from a point of time when a high-pressure discharge lamp starts to light to a point of time when the high-pressure discharge lamp is lighting stably.
As shown in FIG. 6, when the high-pressure discharge lamp starts to light, the high-pressure discharge lamp lighting apparatus applies a high-voltage pulse to the high-pressure discharge lamp through a high-voltage pulse generating circuit to bring the high-pressure discharge lamp into a Townsend discharge state. Then, a current is supplied to the high-pressure discharge lamp through an active filter, a current limiting circuit and an inverter so that the discharge state is shifted from glow discharge to arc discharge to thereby light the high-pressure discharge lamp stably.
As is apparent from FIG. 6, in order to shift the discharge state from the Townsend discharge to stable arc discharge, a voltage not smaller than the peak voltage P of glow discharge must be applied to the high-pressure discharge lamp to go beyond the glow discharge region. In the prior art, however, in use with 100 V, a load current is detected and the boosted voltage is reduced, so that the boosted voltage becomes too low in the glow discharge region to go beyond the glow discharge region and thereby causes light-extinguishing sometimes. Accordingly, the starting property is poor.
Furthermore, the discharge lamp impedance of the high-pressure discharge lamp is low just after the starting of lighting and increases with the passage of time to reach a stable state. If the voltage boosted by the active filter is reduced in the transient process of increasing the discharge lamp impedance, oscillation occurs in feedback control of the current limiting circuit so that the high-pressure discharge lamp may flick or may cause light-extinguishing.
In order to solve the above problems, it is an object of the present invention to provide a high-pressure discharge lamp lighting apparatus adapted to be used in common for several kinds of AC voltages such as 100 V and 200 V, in which not only good starting property can be secured in use at any voltage but also the apparatus can be reduced both in the circuit loss and apparatus size.